A longstanding problem in the art of design of stationary contacts for knife blade switches has been to provide a mechanical apparatus capable of maintaining electrical contact between the jaws of the stationary contact and the switchblades when the switchblades undergo lateral motion under the influence of electromagnetic forces generated during short circuit conditions. Methods tried in the past to solve this longstanding problem have included the use of retention springs on the jaws of a stationary contact. Retention springs used previously include spring clips which slip onto the jaws of a stationary contact and apply force to the jaws.
A disadvantage of the arrangements used previously to maintain electrical contact with the blade of a knife blade switch has been that they have insufficient lateral motion to follow the lateral motion experienced by switchblades during short circuit conditions. The problem is particularly acute in switchblade arrangements designed for medium voltage, that is, voltages of up to 5,000 volts, and ordinary current flows of several hundred Amperes. Short circuit conditions in such apparatus can generate sufficient forces to drive the switchblades of an isolation switch out of contact in the lateral direction with the jaws of the stationary contact, thereby interrupting the current flow, or at least increasing the resistance to the current flow if one of the contacts remains in electrical contact with the switchblades as it undergoes lateral motion.
SUMMARY OF THE INVENTION
The invention solves the problem of loss of contact between jaws of a stationary contact with a switchblade of a knife switch when the switchable undergoes lateral motion, as for example, under the influence of electromagnetic forces during short circuit conditions. A jaw for a switch has a base, a pair of electrically conducting jaws for accepting a blade of a switch between said jaws, a pin mounted in a hole passing through said base; retention springs mounted on said pin and producing force against said jaws so as to maintain electrical contact between said jaws and said switchblades, wherein said pin may slide in said hole in said base so that said jaws may follow lateral motion of said switchblade.
Other and further aspects of the present invention will become apparent in the course of the following description and by reference to the accompanying drawings.